Ordinary impurities 466
a mixture of toluene and isopropyl alcohol (90:10), in a nonequilibrated chamber.
Prepare a filtered and degassed mixture of water, acetonitrile, and glacial acetic acid (800:700:1.5). Make adjustments if necessary (see System Suitability
under Chromatography 621
Internal standard solution
Transfer about 35 mg of progesterone to a 50-mL volumetric flask, add Mobile phase to volume, and mix.
Dissolve an accurately weighed quantity of USP Betamethasone Acetate RS
in Mobile phase,
and quantitatively dilute with Mobile phase
to obtain a solution containing about 0.5 mg per mL. Transfer 10.0 mL of the resulting solution to a 50-mL volumetric flask, add 10.0 mL of Internal standard solution,
dilute with Mobile phase
to volume, and mix to obtain a solution having a known concentration of about 0.1 mg of USP Betamethasone Acetate RS
Transfer about 50 mg of Betamethasone Acetate, accurately weighed, to a 100-mL volumetric flask, add Mobile phase to volume, and mix. Transfer 10.0 mL of the resulting solution to a 50-mL volumetric flask, add 10.0 mL of Internal standard solution, dilute with Mobile phase to volume, and mix.
Chromatographic system (see Chromatography 621)
The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation,
and record the peak responses as directed for Procedure:
the relative retention times are about 3 for progesterone and 1.0 for betamethasone acetate; the resolution, R,
between the analyte and internal standard peaks is not less than 2; and the relative standard deviation for replicate injections is not more than 2.0%.
Separately inject equal volumes (about 25 µL) of the Standard preparation
and the Assay preparation
into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C24
in the portion of Betamethasone Acetate taken by the formula:
500C(RU / RS)
in which C
is the concentration, in mg per mL, of USP Betamethasone Acetate RS
in the Standard preparation;
are the peak response ratios obtained from the Assay preparation
and the Standard preparation,